1. Field of the Invention
The invention relates to an overvoltage protection system with an overvoltage protection element and an ignition aid which triggers the overvoltage protection element, the overvoltage protection element having two main electrodes and an air-breakdown spark gap which acts between the main electrodes.
2. Description of Related Art
Electrical, but especially electronic measurement, control and switching circuits, mainly also telecommunications means and systems, are sensitive to transient overvoltage as can result especially from atmospheric discharges, but also from switching operations and short circuits in power supply grids. This sensitivity has increased to the extent that electronic components, especially transistors and thyristors, are used; mainly integrated circuits which are being increasingly used are greatly endangered by transient overvoltages.
To protect electrical, but especially electronic measurement, control and switching circuits, mainly also telecommunications means and systems, generally wherever electronic circuits are used, against transient overvoltages, overvoltage protection elements and overvoltage protection systems have been developed and have been known for more than twenty years (see, for example, published German patent applications or patents 27 18 188; 29 34 236; 31 01 354; 36 39 533; 37 16 997; 38 12 058; 38 37 051; 39 05 427; 39 10 435; 41 41 681; 41 41 682; 42 36 584; 42 44 051; 44 02 615; 44 35 968; and 44 39 730).
An important component of an overvoltage protection system is at least one overvoltage protection element which operates at a certain overvoltage (operating voltage), and thus, prevents overvoltages which are greater than the operating voltage of the overvoltage protection element from occurring in the area protected by this overvoltage protection element.
Overvoltage protection elements belonging to overvoltage protection systems in a wider sense are also gas-filled surge arresters, inductances, resistances and varistors (or components with similar nonlinear characteristics) which, as hybrid circuits, represent overvoltage protection systems (see, published German patent application 42 36 584). For overvoltage protection systems built in the form of hybrid circuits, there is also a rough protective element provided on the input side and a fine protective element provided on the output side (see, for example, published German patent application 39 05 427). If overvoltage protection systems are to differentiated as "coarse protective elements," on the one hand, and as "fine protective elements," on the other, then an overvoltage protection system of the type to which the present invention is directed is a coarse protective element.
It was mentioned at the start that an overvoltage protection element of the type to which the present invention is directed has two main electrodes, and an air-breakdown spark gap which acts between the main electrodes (see, published German patent applications or patent 37 16 997; 41 41 681; 41 41 682; 42 44 051; 44 02 615; 44 35 968; and 44 39 730). In addition to overvoltage protection elements with an air-breakdown spark gap, there are overvoltage protection elements with an air-flashover spark gap in which, therefore, a creeping discharge occurs when operated (see, published German patent applications 27 18 188; 29 34 236; and 31 01 354).
Overvoltage protection elements with an air-breakdown spark gap, as compared to overvoltage protection elements with an air-flashover spark gap, have the advantage of higher current carrying capacity, but the disadvantage of higher and not especially constant operating voltage. Consequently, various overvoltage protection elements with an air-breakdown spark gap have been developed which have been improved with reference to the operating voltage (see, published German patent applications 41 41 681; 41 41 682; 42 44 051; 44 02 615; 44 35 968; and 44 39 730.) Here, in the area of the primary electrodes or the air-breakdown spark gap which acts between the main electrodes, ignition aids have been produced in various ways, for example, such that at least one ignition aid which triggers a creeping discharge and which projects partially into the air-breakdown spark gap is located between the main electrodes, the ignition aids being made in the manner of a bar of plastic documents (see, published German patent applications 41 41 681, 41 41 682, 42 36 584, and 44 02 615) and the main electrodes can be provided with holes which allow, at the instant of operation of the overvoltage protection elements, i.e., at ignition, the resulting arc to be "activated" next to the holes by a thermal or electrical and/or magnetic pressure and force, so that it wanders away from its origin (see, published German patent application 44 02 615). The ignition aids which were addressed above and which are provided in the known overvoltage protection elements can be called "passive ignition aids," "passive" because they do not themselves respond actively, but respond only due to an overvoltage which occurs on the main electrodes.